1. Field of the Invention
The present invention relates to a liquid developer that comprises a colorant and a liquid for dispersing the colorant and serves to cause the colorant to adhere to a latent image on a latent image carrier and develop the latent image and to an image forming apparatus using such a liquid developer.
2. Description of the Related Art
The conventional liquid developers are known to have a toner, which serves as a colorant, dispersed in a solvent such as a silicone oil. Liquid developers are known to be capable of using toners with a small particle size and obtaining bright images. However, with such liquid developers, if a solvent is present during image fixing, the solvent prevents the toner particles from bonding together and the toner is sometimes not fixed to the recording paper. The resultant problem is that the solvent has to be removed by using a plurality of removal rollers prior to image fixing, thereby increasing the structural complexity of the image forming apparatus using the liquid developer.
Employing photocurable liquids for the solvents is also known. The photocurable liquids have a photopolymerization initiator dissolved in a liquid composed of a monomer or oligomer having carbon-based functional unsaturated groups. If the photocurable liquid is irradiated with light such as UV rays, the photopolymerization initiator induces a radical reaction and the monomer or oligomer having carbon-based functional unsaturated groups is crosslinked and cured. The liquid developers using the photocurable liquids can be fixed to the recording paper together with the solvent and do not require an apparatus for removing the solvent, as the conventional liquid developers. Further, the toner can be fixed to the recording paper by light irradiation alone, conventional fixing of the toner by melting with heat is not required, and energy consumption of the image forming apparatus can be reduced.
However, the monomers or oligomers having carbon-based functional unsaturated groups, such as acrylates, are the substances having polarity. Therefore, the specific resistance of the solvent is low. As a result, the electric charge present on the surface of the latent image carrier moves to the liquid developer and the potential on the latent image carrier decreases, sometimes causing image bleeding or image blurring.
Japanese Patent Application Laid-open No. 2003-57883 describes using a photopolymerization initiator as a material with a high electric resistance, thereby increasing the electric resistance of the photocurable liquid. Such an increase in the electric resistance of the photocurable liquid prevents the decrease in electric potential of the latent image carrier surface and inhibits image bleeding and image blurring.
However, if the electric resistance of the photocurable liquid is increased, the amount of the photocurable liquid that electrostatically adheres to the photosensitive body surface sometimes decreases. The resultant problem is that the sufficient amount of the photocurable liquid is not present on the recording medium during fixing and a sufficient fixing ability cannot be obtained.